U.S. Pat. No. 3,933,116 describes and shows a steering and trim apparatus for a marine device. According to this invention, a propeller shaft bearing box is horizontally pivoted in a gimbal ring, and the ring is vertically pivoted in the gimbal support frame. A tiller is secured on the gimbal ring vertical pivot shaft for horizontally swinging the propeller shaft to control steering. As shown in the drawings of that patent, the steering tiller is brought forward into the hull through an enlarged opening which must be sealed if the hull is submerged below this point. It is also evident in the general arrangement of this invention that the steering tiller is not suitable for counteracting large side forces typically generated by high performance marine outdrives.
U.S. Pat. No. 4,544,362 and U.S. Pat. No. 4,645,463 describe alternative steering and trim apparatuses for marine outdrives. As with U.S. Pat. No. 3,933,116, a telescoping linkage connects the outdrive with the hull and is used to vertically support the outdrive and provide trim capability. One or two additional telescoping linkages are similarly configured on the sides of the outdrive to provide steering capability for the outdrive. In order to provide a reasonable lever arm, the transverse location of the mounting points on the hull must be at a substantial distance from the center of the outdrive. In many applications, space limitations and the typical hull geometry allow only one steering linkage per outdrive to be used. In these cases, a substantial portion of the hydraulic force generated by the steering linkage is not applied in the direction required for steering thereby resulting in a large undesirable force being applied along the axis of the drive. These configurations also result in the hydraulic steering and trim cylinders being exposed to the marine environment and experience undesirable bending and torsional loads in addition to providing forces along the cylinder axis. The hydraulic cylinders, associated with the hydraulic lines and the position sensors, are also exposed to the marine environment.
U.S. Pat. No. 5,290,182 describes an alternative steering and trim apparatus for a marine outdrive which uses a single telescoping link between the outdrive and the hull to provide both trim and steering capability. As with the above discussed prior art, an external hydraulic cylinder is used for providing the trim capability. An external cylinder which must counteract torsional and bending loads from the outdrive and is exposed to the marine environment. A steering lever arm in combination with an “articulation ball” provides an internal tiller arrangement form steering. The “articulation ball” provides sealing for penetration of the tiller arm. It is noted that the combination of a tiller arm and the “articulation ball” results in a side reaction force on the ball whose magnitude is similar to the required steering force at the tiller arm. Designing to accommodate this forces would tend to result in a heavy apparatus for high performance marine outdrives.
U.S. Pat. No. 5,549,493 describes an alternative steering and trim apparatus for a marine outdrive, similar to the above arrangements, but where the single linkage between the outdrive and the hull has a fixed geometry and means are provided for steering and trim with internal mechanisms. This embodiment also uses an “articulating ball which seals the steering arm from the marine environment and absorbs large steering reaction forces. This arrangement has the advantage of moving all hydraulic and position sensor equipment inside the hull and separating those components from the marine environment. However, dealing with the associated design loads results in a fairly heavy apparatus which requires significant interior space.